Contact assembly



July 27, 1937. G. H. `lr--AGLEY- 2,088,411"

CONTACTI ASSEMBLY Filed April 10, 1934 l inventori Gilbert H. Faglefg.

His Attorney.

Patented .iniy 27, 1937 PATENT OFFICE Gilbert n. Fagiey,

General New York Pittsfield, Mass., assignor to Electric Com pany, a corporation of Application April 10, 1934, Serial No. 719,900

3 Claims.

My invention relates to electrical contacts and more particularly to an improved stationary contact assembly for contact making voltmeters.

A contact making voltmeter is. a Voltage responsive circuit controller which is usually used as the master control element of voltage regulating systems of the type employing a tap changing transformer or an induction voltage regulator. It usually comprises a main operating solenoid which is mechanically connected to a pivotally mounted contact beam in such a manner that the beam is rocked or moved onits pivot in accordance with changes in the voltage of a circuit energizing the operating solenoid. The

contact beam usually carries two contacts which cooperate respectively with two stationary contacts. In operation, when the voltage falls below a predetermined value, one of the contacts on the contact beam engages one of the stationary contacts,k thereby completing a ,circuit for causing the regulator to raise the voltage, whereas if the voltage is above a predetermined value the otherV contact of the contact beam engages the other stationary contact, thereby completing a circuitv for causing the regulator to operate in such a manner as to reduce the voltage. There isvusually a small range of motion' of the solenoid and contact beam in which none of the contacts are in engagement and this range corresponds to the voltage band of the regulating system.

One of the main problems encountered in the design and operation of contact making voltmeters is the problem of securing proper and long lived contact action. It has been found that if the stationary contacts are: rigidly mounted there is a tendency f or a contact rebound and contact chattering to take place upon the closing of the contact. This causes contact arcing which is harmful to the contact surface and which also shortens the useful life of the contacts. By resiliently mounting the stationary contacts this rebound and chattering [can be reduced, but wit-h an ordinary resilient mounting there is sufficient counteriorce produced by the resilience of the mounting still to cause some rebound and to throw the movable contacts out of engagement with the stationary contacts before the voltageA has returned to a value within the regulating' r mounting the stationary contacts tend to vibrate,

(Cl. 20G-166) due either to the vibration of the meter itself, when it is energized from anlalternating current circuit, or from the fact'th'at the motion imparted to the stationary contacts by engagement with the Y movable contacts of the contact beam sets the 5 former in lmotion and due to the extreme resilience of thesupport this motion is continued in a vibratory manner for an appreciable time and with an appreciable amplitude of Vibration after the contacts separate.

In accordance with my invention I have provided a simple and novel stationary contact assembly for contact making voltmeters in which the stationary contacts are movable with. the contacts of the contact beam in such a manner as to offer a minimum resistance to Ythis motion and in which means are provided for preventing undesirable vibratory motion'of the stationary contacts. As a result of the oiTering of a minimum of resistance to the motion o-f the contacts of the contact beam, these contacts can always assume.l a position which corresponds to the voltageo the energization oi the operating solenoid and consequently a regulating operation can be completed in a fewer number of Steps than heretofore because of the negligible tendency of Athe stationary contacts to throw the movable contacts away before the regulating change has been completed. Similarly, the minimum resistance to motion of the movable contacts minimizes contactrebound and hence contact arcing. I achieve the above results through the use of an extremely light and resilient supporting means for the stationary contacts combined with a stop member for preventing vibration of the stationary contacts, ,and also through the use of specially constructed stationary ,contacts of extremely light weight.

AnY object of my invention is to provide a new and improved'contactmounting. j

Another object of my invention is to provide a new and improvedV electrical Contact construction.

A further object of my invention isV to provide a new and improved'stationary contactv assembly. for Contact making voltmeters.

My invention will be better understood ,from Ar the following description taken in connection with the accompanying drawing and its scope will be pointed out in the'app'end'ed claims.l y

In the drawing,l in which like reference characters designate similar elements throughout the Y 50 several views, Fig. 1 is a perspective view of the upper portionof a contact making voltmeter embodying the features of my invention; Fig. 2 isa longitudinal sectional view of a preferred form of my improved stationary contact assembly; 55

Fig. 3 is an end view of the contact assembly; Fig. 4 is a bottom View of the assembly and Fig. 5 is a detailed perspective view of one of the stationary contacts.

ReferringI now to the drawing and more particularly to Fig. l, the contact making voltmeter shown therein consists essentially of a base I, on which is mounted an enclosed operatingsolenoid 2 having a core 3 which is connected by means of a resilient operating connection, or spring, 4, to a pivotally mounted contact beam 5 having movable contacts I and 'I carried thereon. Cooperating respectively with movable contacts 6 and 'I are a set of resiliently mounted stationary contacts 8 and 9.

The normal operation of the meter is such that if the energization of the operating solenoid 2 falls below a predetermined value corresponding to a predetermined low voltage the core 3 moves downwardly thereby causing movable contact 'i to engage stationary contact 9, whereas if the energization of the solenoid 2 is above a predetermined value corresponding to a voltage above a predetermined high value, the core 3 moves upwardly thereby causing the movable contact 6 to engage the stationary contact 8.

The contact assemblies for the stationary contacts 8 and 9 are identical and consequently only the details of the contact assembly for stationary contact 8 are shown in the remaining figures. Referring now to Figs. 2, 3, and 4, it will be seen that the assembly for stationary contact 8 comprises an insulating support I to which is fastened by means of a bolt II a strip of metal I2. Fastened to this strip of metal by any suitable means, such as by riveting, is an extremely exible and resilient blade spring I3 to the outer end of which is fastened the contact 8. For preventing vibration of the contact 8 as a result of the extreme resilience of the spring I3 I provide a stop I4 underneath the spring I3 so that when the contact 8 is in normal position the stop I4 bears against the spring I3 and prevents vibration of the contact 8.

One convenient way of combining the strip I2 and stop I4 is to bend the sides of the strip I2 downwardly so as to form side members I and to provide one of these side members with an integral projection which when bent inwardly forms stop member I4. The other projection may be made less wide than I4 so that when bent inwardly it forms a guard member I6 for stop I4. The member I6 is a guard for stop I4 in the sense that it prevents powdered contact metal from getting between spring I3 and its stop I4, as otherwise this powdered metal would cause sticking. In order to increase the resilience and iiexibility of the spring I3, this spring is shown as having a cut-away center section, as can be seen clearly in Fig. 4.

Strip I2 is also provided with a dished-in portion Il which acts as a stop to limit the motion of contact 8 and hence to limit the motion of the contact beam. This limiting of the contact beam motion renders more uniform the action of the usual holding coils, which are shown enclosed at I8 and I9 respectively.

I have found that if the blade spring I3 and the stop I4 are made of different metals,v some reaction takes place between these two metals which appears to be a sort of electrolytic reaction or form of thermocouple eifect, and after a short time the spring tends to adhere slightly to the stop so that the stationary contact is not lifted away by the torque obtained from the solenoid under normal voltage changes. Such a reaction may be prevented in numerous ways, such as providing the stops with glass beads or other similar material, but I have found that if the spring and stop are made of the same metal, this action does not take place, and the metal which I at present prefer to employ is stainless steel for both blade spring I3 and the stop I4.

In order further to improve the operation of the meter and increase its accuracy, I construct the stationary contacts in a special manner. As shown more clearly in Fig. 5, this contact is of hollowed out construction. This decreases its weight, whereby it is more easily moved by the force produced by the operating solenoid, thus further reducing the tendency of contact rebound to occur. In the form which I at present contemplate employing, the stationary contactI 8 is a cup-shaped piece of metal having a rounded bottom or contact surface roughly conforming to the shape of a sphere and having cut away side faces. This cutting away of the side faces produces two distinct advantages. The rst is, that it provides openings between the inside of the contact and the atmosphere so that air may pass therethrough thereby providing ventilation and cooling of the contacts, which is important, since there is more tendency for the contact to become heated for a given current by reason of the reduced conducting cross section resulting from its hollow form. The second advantage of the cutaway side faces is that it provides at least two separate Vsurfaces in the same plane for attachment to the blade spring I3. I have found that if the surface for attachment to the blade spring is circular, it is very difficult to obtain a satisfactory and strong weld between the contact and the blade spring, and as welding is the means which I at present prefer to employ for fastening the stationary contact to the blade spring, it is obviously important that a satisfactory weld be produced. However, by providing two surfaces, or a discontinuous circular surface, a strong weld is produced between each separate surface and the spring I3.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that changes and modications may be made without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A stationary contact assembly for use in contact making voltmeters comprising, in combination, a normally horizontally supported strip of metal having integral downwardly bent sides, inwardly bent projections on said sides, a relatively thin blade spring fastened to said strip so as to pass between said strip and said projections and normally adapted to rest against one of' said projections as a stop, the other projection forming a guard member for said stop, and a contact carried by said spring, said projection which forms a guard member extending between said contact and the other projection which forms the stop. Y

2. A stationary contact assembly for use in contact making voltmeters comprising, in combination, a normally horizontally supported strip of stainless steel having integral downwardly bent sides, an inwardly bent projection on one of said Sides, a thin blade spring of stainless steel of the being of hollow construction so as to reduce its same composition as said strip fastened to said weight thereby improving the accuracy of the strip so as to extend between said projection and meter, said contact also having Ventilating opensaid strip and normally resting in a substantially ings therein, a thin blade spring supporting said 5 unstressed condition on said projection as a stop, stationary contact, saidspring kbeing so resilientl and a hollow contact with Ventilating openings as to offer a negligible resistance to the motion of therein fastened to the under side of said spring. said stationary contact, and a stop placed under 3. In a contact' making voltmeter having an said spring for partially supporting it in a suboperating solenoid and a pivoted contact beam stantially unstressed condition and preventing vi- 10 connected to be rocked by said solenoid, the combration of said contact as a result of the extreme 10 bination of a stationary contact for cooperation resilience of said spring. with said contact beam, said stationary contact GILBERT H. FAGLEY. 

